The Flat Creek-Iron Mountain Mine started when the ore body was discovered by L.T. Jones in 1888.  It was claimed by Jones and his partners as the Iron Mountain and Iron Tower lode claims. The mine was operated by the Iron Mountain Mining Company between 1888 and 1896.  In 1897, the property was closed down by the Inspector of Mines for violations of state law for not having two openings. Then, in 1915, H.L. Day acquired the property.

The mine saw continuous production between 1909 and 1930, with peaks in the mid-1910s and 1920s.  Since then, lessees from time to time have opened the property.  From 1909 to 1953, the Iron Mountain Mine produced 7,535,084 pounds of zinc, 5,385,741 pounds of lead, 5,274 pounds of copper, 389,355 fine ounces of silver, and 19 fine ounces of gold. A lead-antimony sulfosalt in the zinc vein of the Iron Mountain Mine was described as “unique” in the veins of this area. 

ASARCO was the last owner of the mine and have participated in the sites cleanup. The company filed for bankruptcy in 2009 and as part of that agreement, paid $1.9 million to the Montana Environmental Trust Group, LLC (METG).  They also paid $1.7 million to the Montana Department of Environmental Quality in a separate bankruptcy claim.  The US Forest Service was also paid $500,000 by ASARCO to address land administered by the Forest Service. The property, which includes the source of the tailings and the tailings along the Marietta Claim, was then transferred to the METG. The study area that is part of the Superfund site, is located from the USFS/Marietta Claim boundary, which is approximately two miles above the Flat Creek confluence with the Clark Fork River to the Hall/Gulch Flat Creek confluence, which is about four and half miles upstream from the mouth of Flat Creek.  Flat Creek is located four miles northeast of Superior. The lower two miles of the creek are currently owned by the USFS. The upper stream is owned by the Montana Environmental Custodial Trust.